Re: [RFC PATCH v2] media: rcar-vin: Allow independent VIN link enablement

[Steve Longerbeam]

On 1/9/19 2:40 PM, Niklas SÃderlund wrote:
> Hi Steve,
>
> Thanks for your patch, I think it looks good.

Thanks for the Ack! I'm not real familiar with the RFC patch process. 
Should this be submitted again with RFC stripped from the subject line?

Steve

> On 2019-01-06 13:20:18 -0800, Steve Longerbeam wrote:
> > There is a block of code in rvin_group_link_notify() that loops through
> > all entities in the media graph, and prevents enabling a link to a VIN
> > node if any entity is in use. This prevents enabling a VIN link even if
> > there is an in-use entity somewhere in the graph that is independent of
> > the link's pipeline.
> >
> > For example, the code will prevent enabling a link from the first
> > rcar-csi2 receiver to a VIN node even if there is an enabled link
> > somewhere far upstream on the second independent rcar-csi2 receiver
> > pipeline.
> >
> > If this code is meant to prevent modifying a link if any entity in the
> > graph is actively involved in streaming (because modifying the CHSEL
> > register fields can disrupt any/all running streams), then the entities
> > stream counts should be checked rather than the use counts.
> >
> > (There is already such a check in __media_entity_setup_link() that verifies
> > the stream_count of the link's source and sink entities are both zero,
> > but that is insufficient, since there should be no running streams in
> > the entire graph).
> >
> > Modify the media_device_for_each_entity() loop to check the entity
> > stream_count instead of the use_count, and elaborate on the comment.
> > VIN node links can now be enabled even if there are other independent
> > in-use entities that are not streaming.
> >
> > Fixes: c0cc5aef31 ("media: rcar-vin: add link notify for Gen3")
> >
> > Signed-off-by: Steve Longerbeam <slongerbeam@xxxxxxxxx>
> Reviewed-by: Niklas SÃderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
>
> > ---
> > Changes in v2:
> > - bring back the media_device_for_each_entity() loop but check the
> >    stream_count not the use_count.
> > ---
> >   drivers/media/platform/rcar-vin/rcar-core.c | 8 ++++++--
> >   1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/media/platform/rcar-vin/rcar-core.c b/drivers/media/platform/rcar-vin/rcar-core.c
> > index f0719ce24b97..6dd6b11c1b2b 100644
> > --- a/drivers/media/platform/rcar-vin/rcar-core.c
> > +++ b/drivers/media/platform/rcar-vin/rcar-core.c
> > @@ -131,9 +131,13 @@ static int rvin_group_link_notify(struct media_link *link, u32 flags,
> >   	    !is_media_entity_v4l2_video_device(link->sink->entity))
> >   		return 0;
> >   
> > -	/* If any entity is in use don't allow link changes. */
> > +	/*
> > +	 * Don't allow link changes if any entity in the graph is
> > +	 * streaming, because modifying the CHSEL register fields
> > +	 * can disrupt running streams.
> > +	 */
> >   	media_device_for_each_entity(entity, &group->mdev)
> > -		if (entity->use_count)
> > +		if (entity->stream_count)
> >   			return -EBUSY;
> >   
> >   	mutex_lock(&group->lock);
> > --
> > 2.17.1